symtbl: Refactor abstract IndexTbl interface

There are some useful concepts expressed in the Symtbl class that can
provide good value if applied elsewhere as well.  In this particular
case, I want to address the somewhat awkward relationship between Symtbl
and the Payload class by providing an abstract base for both of them.  I
will go into more details in an upcoming commit for Payload.

This patch shouldn't change any behavior for Symtbl barring perhaps its
new preference of the new IndexEntry type described below.  Some
characteristics of Symtbl are refactored into two new interface types:

IndexEntry provides "base" and implements logic supporting the use of
instance objects as integers.  The intent is to extend from this class
when creating special types to be used in IndexTbls, Symtbls, etc.

IndexTbl (extends IndexEntry) provides a unified system for attribute /
element access, and acts as an abstract container where storage and
lookup semantics are up to the specific implementation.

Symtbl (extends IndexTbl) is now better described as an Index table,
where indices represent numeric addresses.  The nominal data type is
int, however IndexEntries (which are int-like) may be nested to record
the addresses of ROP gadgets, sub-symtbls, and perhaps more in the
future.

Signed-off-by: Malfurious <m@lfurio.us>

1 files changed, 103 insertions, 0 deletions

diff --git a/sploit/types/indextbl.py b/sploit/types/indextbl.py
new file mode 100644
index 0000000..4f57a59
--- /dev/null
+++ b/sploit/types/indextbl.py
@@ -0,0 +1,103 @@
+from abc import abstractmethod
+from collections.abc import Collection
+
+from sploit.types.index_entry import IndexEntry
+
+class IndexTbl(IndexEntry, Collection):
+    """
+    Abstract Index Table
+
+    IndexTbl is a common interface to an abstracted key-value store.  The
+    storage mechanism as well as lookup semantics are defined by concrete
+    implementations.  "Index" in this case is more akin to a directory index or
+    book index than a strictly numeric array index.
+
+    In general, concrete tables may store values of any or multiple different
+    types.  In particular, tables should give special accommodation for values
+    of type IndexEntry.  These objects usually represent "rich" versions of the
+    nominal data types the table expects to contain.  Implementation repr()
+    methods usually also annotate which members are IndexEntries.
+
+    IndexTbl extends from IndexEntry, and so has a base value which represents
+    the "base index" of the table.  The meaning of this depends on the
+    implementation.  This inheritance also means that tables are generally
+    expected to be nestable.
+
+    IndexTbls allow indices to be accessed via attribute or subscript notation.
+    This is probably the key characteristic feature of the class.  The class
+    namespace is kept as clean as possible to make for the fewest collisions
+    between index names and other (real) class attributes.  Note that there are
+    abstract methods, required to be overridden, which implement the index
+    access.  These methods are only called for normal indices, not the table
+    base.
+
+    Because this class overrides attribute access, normal automatic object
+    copying is broken.  Because of this, implementations must also provide a
+    definition for the __copy__() method as well.
+    """
+
+    @abstractmethod
+    def __getindex__(self, index):
+        """Lookup and retrieve index value."""
+        raise NotImplementedError
+
+    @abstractmethod
+    def __setindex__(self, index, value):
+        """Lookup and set index value."""
+        raise NotImplementedError
+
+    @abstractmethod
+    def __delindex__(self, index):
+        """Lookup and delete index value."""
+        raise NotImplementedError
+
+    @abstractmethod
+    def __copy__(self):
+        """Create a copy of this IndexTbl object."""
+        raise NotImplementedError
+
+    def __contains__(self, index):
+        """Test the existence of the given index."""
+        try:
+            self.__getindex__(index)
+        except KeyError:
+            return False
+        else:
+            return True
+
+    # Attribute access methods
+
+    def __getattr__(self, index):
+        """Get value via attribute."""
+        return self[index]
+
+    def __setattr__(self, index, value):
+        """Set value via attribute."""
+        self[index] = value
+
+    def __delattr__(self, index):
+        """Delete value via attribute."""
+        del self[index]
+
+    # Subscript/item access methods
+
+    def __getitem__(self, index):
+        """Get value via subscript."""
+        if index == "base":
+            return self.base
+        return self.__getindex__(index)
+
+    def __setitem__(self, index, value):
+        """Set value via subscript."""
+        if index == "base":
+            object.__setattr__(self, "base", value)
+        elif index in dir(self):
+            raise KeyError(f"IndexTbl: Index is reserved: {index}")
+        else:
+            self.__setindex__(index, value)
+
+    def __delitem__(self, index):
+        """Delete value via subscript."""
+        if index == "base":
+            raise KeyError("IndexTbl: May not delete index: base")
+        self.__delindex__(index)